The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Aspects of the invention relate to a system for mooring a vessel at an offshore site.
For the offloading of tankers, in particular those that carry Liquefied Natural gas (LNG), it is at times advantageous if they can be moored offshore, in a safe and expedient manner, such that offloading can be performed well away from congested harbour and populated areas. Examples of such offshore offloading systems are known, e.g. the “Accelerate” on-board regasification project in the Gulf of Mexico. Such systems have not found application in a widespread manner.
The major issues in offloading such LNG tanker offshore are many.
For instance, to date, there are only a few (i.e. less than 1%) LNG tankers outfitted with re-gasification equipment. Gasification requires an expensive extension to each vessel such as to be able to re-gasify the cargo on board and this equipment is only required for typically 3 days per, say, 3 weeks and hence is cost-inefficient. It is much more efficient if LNG could be offloaded without the need for onboard re-gasification.
Multibuoy moorings have been in use in the offshore oil industry for decades and various vendors supply these systems, but they all suffer from significant drawbacks if bigger ships have to be moored. It takes generally many hours to fit the mooring lines between the ship and the buoys. If any of those lines was to disconnect during the offloading a dangerous situation could occur which could even lead to collision between the vessel and any the offloading equipment near the water surface.
For these reasons, most, if not all, present LNG terminals are located inside protected waters, some distance away from population centers. A standard quayside/pier arrangement is then used, such as shown in FIG. 1 of U.S. Pat. No. 6,886,611, employing rubber fenders and nylon or polyester mooring ropes to secure the vessel to the quay/pier.
Since the amount of LNG import is rising dramatically, a significant shortage of suitable vessel berths will occur in the next decade, a shortage which can be mitigated by mooring and offloading such vessels offshore.